We used Highrise for a while; it's a nice and simple web-based app that will work on any device: http://highrisehq.com/

We have since switched to SalesForce, but afaik we're not really power-using it so I can't comment on what is better.

After absorbing a lot of MS PR recently I feel like if you're an Office/Outlook/Exchange shop, Dynamics is probably worth a very close look - it sounds cheaper per seat than the options (although maybe that is only in large scale).

We've been using Capsule, which has been okay thus far. Though we're about 95% of the way through developing our own awesome one. Wish I could say we're finished for threads like this >:( ticks all your boxes